1. Field of the Invention
This invention relates to a position measurement system of projecting a concentric pattern, detecting the concentric pattern by a sensor, and measuring the position of the sensor and the normal direction of the sensor plane. The position measurement system can be used as a sensor installing pointer, a position information system, etc., for example.
2. Description of the Related Art
To measure the position of an object with high accuracy in three-dimensional position measurement, for example, a measurement method using interference of light is used; however, this kind of related art involves the following problems: The cost of the parts of an interference optical system is high; the position accuracy required for assembling is high; the number of parts is large and a number of assembling steps is required; the method (art) is unfitted for position measurement of a mobile unit, etc.
Then, for example, JP-A-2004-28977 proposes a position measurement system capable of executing position measurement using interference of light at a low cost in a simple configuration. The system can be used as a pointer system, for example. In the pointer system, a device for projecting a concentric pattern is used as a pointer and a sensor is installed in the proximity of an object pointed to by the pointer, for example, a display. If the user points to the object by the pointer, the concentric pattern projected by the pointer is detected by the sensor, the center point of the concentric pattern is calculated using an arithmetic unit from the detection information, and a cursor is displayed on the display, for example, with the center point as the point pointed to by the pointer.
In this method, however, only one user can use the system and it is difficult for a plurality of persons to use respective pointers at the same time; this is a problem. To identify the users of a plurality of pointers, it is necessary to carry a modulation signal on light emitted by each pointer and install a function of identifying the light (modulation signal) in the light receiving party; this is also a problem. Thus, the pointer system in the related art is a system used by one user and it is virtually impossible for a plurality of persons to use respective pointers at the same time. The method of assigning ID to each pointer and identifying it is complicated.